[SciPy-User] wrong output shape calculation in scipy.ndimage.interpolation.zoom

Matthieu Rigal rigal@rapideye...
Mon Aug 1 12:47:30 CDT 2011


Hi guys,

I just detected a problem with the output shape calculation when running a 
zoom function.
Sometimes it returns an odd value, here is an example :
>>> import numpy
>>> from scipy.ndimage.interpolation import zoom
>>> aT = numpy.ones((5000,5000))
>>> aT2 = numpy.ones((556,463))
>>> aT3 = zoom(aT2, (float(aT.shape[0])/aT2.shape[0], 
float(aT.shape[1])/aT2.shape[1]))
>>> aT3.shape
(4999, 5000)

Whereas adding a very little incrementation factor produces it right :
>>> aT3 = zoom(aT2, (1.00001*float(aT.shape[0])/aT2.shape[0], 
1.00001*float(aT.shape[1])/aT2.shape[1]))
>>> aT3.shape
(5000, 5000)

There must be somewhere a problem with the roundings... should I file a ticket 
?

Regards,
Matthieu

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